CHLORINE. CALCULATIONS 



147 



minutes, chlorine ceases to be dissolved in the test-tube, and 

 the gases come off in their natural proportions. In half-an-hour 

 more they have filled the tube. The stop cocks are now closed, 

 the tube is set in a tall cylinder containing potas- 

 sium iodide (KI) solution (Fig. 52) and the lower 

 stop cock is opened. The potassium iodide acts 

 upon the chlorine, giving potassium chloride and 

 free iodine which is a solid, 



2KI + C1 2 -* 2KC1 + I, 



and the liquid rises until it fills half the tube. The 

 remaining gas burns and is hydrogen. 



The volume of the hydrogen chloride, in relation to 

 the volumes of the constituents, may be learned 

 by using a different apparatus (Fig. 53). A test- 

 tube of heavy glass is filled with dry hydrogen 

 chloride and closed with a rubber stopper greased 

 with vaseline. A little sodium amalgam (solution 

 ^ of sodium in mercury) is in- 

 troduced, and the stopper in- 

 stantly replaced. When the 

 contents are shaken for one FlG ' 52 

 or two minutes, the sodium combines with 

 the chlorine and the hydrogen is liberated 

 and remains. The mouth of the test-tube 

 is then immersed in a jar of mercury, and 

 the stopper withdrawn. The mercury rises 

 and fills about half the tube. 



Conclusion. The hydrogen has half the 

 volume of the hydrogen chloride, and the volume of the chlorine 

 is equal to that of the hydrogen. Therefore: 



1 vol. hydrogen -f 1 vol. chlorine > 2 vols. hydrogen chloride. 



FIG. 53 



This result further illustrates Gay-Lussac's law (p. 60). 



